1. Field of the Invention
This invention relates generally to monitoring means for measuring the vacuum in vacuum devices and more particularly to measuring the degree of the vacuum in vacuum circuit interrupters.
2. Description of the Prior Art
The desirable characteristics of a vacuum as a dielectric medium have resulted in increasing use of vacuum circuit interrupters as protective devices in power distribution networks. Maintaining the vacuum in the interrupter is critical for safe and reliable operation. Consequently, power system engineers have been attempting to develop more effective and reliable means to monitor the internal pressure of the vacuum circuit interrupter.
A patent of interest is U.S. Pat. No. 3,403,297 entitled "Vacuum-Type Circuit Interrupter with Pressure-Monitoring Means" issued to D. W. Crouch, Sept. 24, 1968, discloses a vacuum monitoring means using a high potential to ignite a discharge within the vacuum. Other patents of interest are U.S. Pat. No. 3,575,656, issued Apr. 20, 1971; U.S. Pat. No. 3,263,162 issued July 26, 1966; and U.S. Pat. No. 4,000,457 issued Dec. 28, 1976, all of which employ cold cathode ionization gauges for monitoring the vacuum.